Figure 7.

(a) Skeletal arrangement of the avian leg, body and wing. (b,c) Abstracted multi-body simulation model comprising rigid segments connected by actuated 1 d.f. revolute joints at the hip, knee, ankle, tarsometatarsal (TMT) joint and elbow, a 2 d.f. universal joint wrist, and a 3 d.f. spherical joint at the shoulder. (b) The perch model constrains the functional foot (digits) to remain stationary on the perch. (c) The ground model uses two contact points (filled circles) positioned at the rear and front toe to apply ground reaction forces when in contact with the ground. In the perch model (figure 7b), it is assumed that the functional foot can provide sufficient friction to prevent rotation around the perch, so the foot remains stationary throughout the jump. The perch model captures the countermovement and acceleration dynamics up until the time when the digits begin to disengage from the perch just prior to take-off.